Battery protection systems for detecting conductive liquid ingress and associated devices and methods

ABSTRACT

This application is directed to an electronic device powered by one or more rechargeable battery cells. The electronic device includes a first negative temperature coefficient (NTC) thermistor proximate to the battery cells, and an open capacitor coupled in parallel with the NTC thermistor. The open capacitor has an open area and two electrodes that are at least partially exposed via the open area and electrically isolated. The electronic device further includes a control circuit coupled to the NTC thermistor and the open capacitor. The control circuit is configured to detect a voltage drop across the NTC thermistor and the open capacitor if conductive liquid enters the open area of the capacitor and electrically connects the two electrodes that are at least partially exposed via the open area.

TECHNICAL FIELD

This application relates generally to battery technology including, butnot limited to, methods and systems for detecting exposure of arechargeable battery of an electronic device to conductive liquid andprotecting the rechargeable battery from damage caused by such exposure.

BACKGROUND

Integrated lithium-ion battery packs are commonly used in electronicdevices. If a lithium-ion battery pack (e.g., battery cell(s) and areasof its protection circuit module (PCM)) is exposed to water, corrosionfrom the water may result in cell swelling and circuit failure. In manyoutdoor applications (e.g., in outdoor cameras), mechanical seals areapplied along with water detection mechanisms to prevent water ingressinto the lithium-ion battery packs of the electronic devices. However,many of these solutions are expensive and complicated, nor can theyprovide a sufficient sensitivity to water or stop water ingressentirely. Therefore, there is a need for simple and cost-effectivesolutions of detecting water ingress into lithium-ion battery packs ofelectronic devices, thereby protecting the lithium-ion battery packsfrom further damage caused by the water ingress.

SUMMARY

This disclosure describes methods and systems for a battery pack of anelectronic device that includes one or more rechargeable battery cellsand a self-contained battery protection system for detecting conductiveliquid ingress. The battery protection system includes a capacitorhaving open metal gaps (e.g., interdigitated pads) and electricallycoupled in parallel with a negative thermal temperature coefficient(NTC) thermistor. If water ingress occurs at a battery pack level, itcauses a change associated with the NTC thermistor to go beyond or actdifferently in a normal range associated with a battery temperaturevariation. The change associated with the NTC thermistor is one of avoltage drop across the NTC thermistor and a resistance drop of acombination of the NTC thermistor and the open metal gaps. Such a changeassociated with the NTC thermistor is compared to a predefined referencevalue or to a reference change measured from a reference NTC thermistor.

In some implementations, in accordance with a determination that a rateof a change of temperature in the NTC thermistor exceeds a thresholdrate (e.g., 10° C. for one hour duration) or is distinct from that ofthe reference NTC thermistor, the electronic device determines that sucha rate of the temperature change is caused by water ingress, and shutsdown the rechargeable battery to prevent damage to the battery. In someimplementations, in accordance with a determination that a correspondingtemperature detected from the NTC thermistor exceeds a thresholdtemperature (e.g., exceeds 100° C.) or distinct from that detected fromthe reference NTC thermistor, the electronic device determines thatdetection of such a battery temperature is caused by water ingress, andthus, locks out the battery by disabling discharge charge field effecttransistors (FETs) that are electrically coupled to the battery. In somesituations, the battery protection system enables a three-way fuse FETto blow an internal fuse and disconnect the battery from the electronicdevice permanently.

In one aspect, some implementations include an electronic device thatincludes one or more rechargeable battery cells. The battery cells areconfigured to power operation of the electronic device. The electronicdevice also includes a negative temperature coefficient (NTC) thermistorproximate to the battery cells. The electric device also includes acapacitor coupled in parallel with the NTC thermistor. The capacitor hasan open area and two electrodes that are at least partially exposed viathe open area. The electrodes are electrically isolated. The electronicdevice further includes control circuit coupled to the NTC thermistorand the capacitor. The control circuit is configured to detect a voltagedrop across the NTC thermistor and the capacitor if conductive liquidelectrically connects the two electrodes that are at least partiallyexposed via the open area. In some implementations, the two electrodesof the capacitor are interdigitated and formed with the same conductivelayer on a substrate, and at least partially overlap the open area.

In another aspect, some implementations include a battery protectioncircuit coupled to one or more rechargeable battery cells. The batteryprotection circuit includes an NTC thermistor proximate to the one ormore rechargeable battery cells. The battery protection circuit alsoincludes a capacitor coupled in parallel with the NTC thermistor. Thecapacitor has an open area and two electrodes that are at leastpartially exposed via the open area. The two electrodes are electricallyisolated. The battery protection circuit also includes a control circuitcoupled to the NTC thermistor and the capacitor. The control circuit isconfigured to detect a voltage drop across the NTC thermistor and thecapacitor if conductive liquid electrically connects the two electrodesthat are at least partially exposed via the open area.

In yet another aspect, a method is implemented to reconfigure arechargeable battery to detect conductive liquid. The method includesproviding a capacitor to be coupled in parallel with an NTC thermistorthat is proximate to one or more rechargeable battery cells of anelectronic device. The capacitor has an open area and two electrodesthat are at least partially exposed via the open area, and the twoelectrodes are electrically isolated and configured to be coupled whenconductive liquid enters the open area of the capacitor. A controlcircuit is coupled to the NTC thermistor and is configured to detect avoltage drop across the NTC thermistor and the capacitor and determinewhether the voltage drop is caused by conductive liquid entering theopen area of the capacitor.

In yet another aspect, a method is implemented to detect conductiveliquid in a rechargeable battery. The method includes receiving avoltage drop across an NTC thermistor and a capacitor that are proximateto one or more rechargeable battery cells. The capacitor has an openarea and two electrodes that are at least partially exposed via the openarea, and the two electrodes are electrically isolated. The methodfurther includes determining whether the voltage drop is caused byconductive liquid that electrically connects the two electrodes that areat least partially exposed via the open area of the capacitor.

Systems, devices, and methods are provided to supplement an integratedrechargeable battery with a capacitor that is coupled in parallel withan existing NTC thermistor, thereby allowing detection of conductiveliquid in the integrated rechargeable battery without or with littlechange to existing architecture and configuration of the batteryprotection system. As such, this application provides simple andcost-effective solutions of detecting water ingress into integratedbattery packs of electronic devices and protecting the integratedbattery packs from further damage caused by the water ingress.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described implementations,reference should be made to the Detailed Description below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1A illustrates an electronic device including a rechargeablebattery in accordance with some implementations, and FIG. 1B is a blockdiagram of an electronic system including an electronic device coupledto an external power source, in accordance with some implementations.

FIG. 2A is a schematic diagram of an example rechargeable battery (alsocalled a battery pack) having a battery protection system coupled to oneor more battery cells, in accordance with some implementations, and FIG.2B illustrates an example open capacitor, in accordance with someimplementations.

FIG. 3 is a schematic diagram of another example rechargeable batteryhaving a battery protection system coupled to one or more battery cells,in accordance with some implementations.

FIG. 4 illustrates another example open capacitor having interdigitatedelectrodes, in accordance with some implementations.

FIG. 5 is a schematic diagram of an electronic system having a batterycoupled to a charger, in accordance with some implementations.

FIG. 6 is a table of example resistivity values of known conductiveliquid types, in accordance with some implementations.

FIG. 7 illustrates a temporal diagram of an effective resistance of anNTC thermistor that is coupled in parallel with a capacitor, inaccordance with some implementations.

FIG. 8A is a diagram of an effective resistance of an NTC thermistorthat varies with a temperature, in accordance with some implementations,and FIG. 8B is a diagram of a temperature sensitivity of an NTCthermistor that varies with a temperature, in accordance with someimplementations.

FIG. 9 is a flowchart of an example method of detecting conductiveliquid in a rechargeable battery, in accordance with someimplementations.

Like reference numerals refer to corresponding parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION

FIG. 1A shows an electronic device 100 including a rechargeable battery102 in accordance with some implementations. The electronic device 100can be a camera as shown, or a doorbell, door lock, display, connectedassistant device, alarm, hazard detector, security detector, thermostat,or any other type of electronic device that is powered by a rechargeablebattery 102. In some implementations, the electronic device 100 is usedfor outdoor applications. The electronic device 100 may include one ormore mechanical seals for preventing water ingress. In someimplementations, the electronic device 100 includes one or morecomponents, such as: audio devices, light sources, sensors, centralprocessing unit(s) (e.g., CPU(s) 114 in FIG. 1B), memory, data inputdevices, data output devices, image sensor array, infrared illuminators,filters, and at least a subset of the one or more components is poweredby the rechargeable battery 102. In some implementations, the electronicdevice 100 is configured to connect electronically with an externaldevice through a wired connection (e.g., a Universal Serial Bus (USB)cable, a power cable, a High-Definition Multimedia Interface (HDMI)cable, etc.). The wired connection may allow power and/or datatransmission between the external device and electronic device 100. Forexample, the wired connection can be used to provide power to thebattery 102.

Alternatively or additionally, in some implementations, the electronicdevice 100 includes one or more (external and/or visible) ports orconnectors 110 for wired connections to the various components of theelectronic device 100. Examples of the one or more ports or connectors110 include, but are not limited to, USB connectors, and DC powerconnectors. In some implementations, the one or more ports 110 are on asurface of the electronic device 100 and allow for external access tothe various components of the electronic device 100. In someimplementations, the one or more ports 110 of the electronic device 100can be used to charge the battery 102. For example, a wired connectionis formed between the port 110 of the electronic device 100 and anexternal power source (e.g., a portable power cell, power generator,power bank, etc.), and can be used to transfer power from the externalpower source to the battery 102.

FIG. 1B illustrates a block diagram of an electronic system 150including an electronic device 100 coupled to an external power source108, in accordance with some implementations. The electronic device 100includes a rechargeable battery 102 having one or more battery cells 120and a battery protection system 104. In some implementations, therechargeable battery 102 is built into the electronic device 100 or is areplaceable module in the electronic device 100. In someimplementations, the battery 102 includes a single rechargeable batterycell 120. In some implementations, the battery 102 includes a pluralityof rechargeable battery cells 120 electrically coupled to each other.For example, the plurality of rechargeable battery cells 120 of thebattery 102 can be coupled according to a 1SnP parallel batteryconfiguration, in which n is an integer indicating a number of batterycells connected in parallel (e.g., 1S2P, 1S3P, 1S4P); an mS1P serialbattery configuration, in which m is an integer indicating a number ofbattery cells connected in series (e.g., 2S1P); or an mSnP mixed batteryconfiguration. In this application, the battery 102 broadly refers to abattery pack 102 that packages the one or more battery cells 120 withadditional functional components (e.g., an NTC thermistor, the batteryprotection system 104, a battery heating element).

In some implementations, the one or more battery cells 120 areelectrically coupled to the battery protection system 104 and aninternal circuit 106. The internal circuit 106 includes variouscomponents of the electronic device 100, such as memory 112, CPU(s) 114,data input device(s), data output device(s), lens assemblies, heatsink(s), image sensor array(s), infrared illuminator(s), filter(s). Insome implementations, an external power source 108 is coupled to thebattery 102 and the internal circuit 106. The external power source 108is used to charge the battery 102 of the electronic device 100. In someimplementations, the one or more battery cells 120 and the batteryprotection system 104 are integrated into a single package/enclosurecontained within the electronic device 100. In other implementations,the one or more battery cells 120 and the battery protection system 104are packaged as distinct packages/components within the electronicdevice 100.

In some implementations, the battery protection system 104 is configuredto protect the one or more battery cells 120 while the electronic device100 is being charged by the external power source 108 and/or any otherelectrical source and/or while the battery 102 is being discharged todrive the internal circuit 106 of the electronic device 100. In someimplementations, the battery protection system 104 is used to detectwhen at least one rechargeable battery cell 120 of the plurality ofrechargeable battery cells that belong to the battery 102 disconnects orfails to charge. In some implementations, the battery protection system104 is designed within a protection circuit module (PCM) of the battery102.

In some implementations, the battery protection system 104 includes acapacitor that is packaged inside the battery 102. When electrodes ofthe capacitor are electrically coupled by the conductive liquid, thebattery protection system 104 or the internal circuit 106 can detectconductive liquid entering the battery 102. In some implementations, inaccordance with the detection of the conductive liquid, the batteryprotection system 104 or the internal circuit 106 may intervene (e.g.,disable charging of the battery 102) to protect the battery 102 fromdamage to be caused by the conductive liquid. Additionally, in someimplementations, upon detecting the conductive liquid entering thebattery 102, the electronic device 100 generates a warning messageindicating that the battery 102 has been exposed to the conductiveliquid. The warning message is optionally broadcast via a speaker of theelectronic device 100 or communicated to a client device via one or morecommunication networks for display on a user application executed on theclient device.

FIG. 2A is a schematic diagram of an example rechargeable battery 102(also called a battery pack) having a battery protection system 104coupled to one or more battery cells 120, in accordance with someimplementations, and FIG. 2B illustrates an example open capacitor 210,in accordance with some implementations. The battery protection system104 is configured to determine whether the battery 102 is functioningabnormally and disconnect the battery 102 upon detection of an abnormalcondition (e.g., an overvoltage, undervoltage, overcurrent, or shortcircuit condition) of the battery 102. The battery protection system 104includes a protection integrated circuit (PIC) 202 and a switchingcomponent 206. The PIC 202 is a coupled to the switching component 206,and configured to control charging and discharging of the one or morebattery cells 120 via the switching component 206. In someimplementations, the switching component 206 includes two switches 206 aand 206 b that are coupled in series with each other and with the one ormore battery cells 120 along a charging and discharging path 220. Forexample, the two switches 206 a and 206 b are two integrated fieldeffect transistors (FET) coupled back to back or a dual channelintegrated FET. The switches 206 a and 206 b are controlled by the PIC202 to manage charging and discharging of the one or more battery cells120 separately. In some implementations now shown, the batteryprotection system 104 further includes a second PIC and a secondswitching component. The switch components are coupled in series witheach other and with the one or more battery cells 120 along the chargingand discharging path 220. Each switch component is controlled by acorresponding PIC to manage charging and discharging of the battery 102.

In some implementations, the battery protection system 104 furtherincludes a positive thermal coefficient (PTC) resistor 204. A resistanceof the PTC resistor 204 is low during normal operation of the battery102 and increases to reduce a charging or discharging current flow whenan operating temperature of the battery 102 increases above a thresholdcurrent level. In some implementations, the battery protection system104 further includes a resettable fuse 204 in place of the PTC resistor204.

In some implementations, the battery protection system 104 includes anegative thermal coefficient (NTC) thermistor 208 (e.g., a charger ICNTC thermistor). The NTC thermistor 208 is coupled between an NTCterminal 230 and a supply terminal 224, and has a resistance R_(NTC)configured to vary with the operating temperature of the battery 102. Anoutput of the NTC terminal 230 coupled to the NTC thermistor 208 is usedto monitor the operating temperature of the battery 102 and determinewhether the operating temperature is lower than a threshold temperature.Further, in some implementations, the NTC thermistor 208 is coupled inseries with a reference resistor 216. The reference resistor 216 and theNTC thermistor 208 are electrically biased between two supply voltages(e.g., coupled to two supply terminals 222 and 224). The referenceresistor 216 has a second resistance R_(REF) that remains substantiallyconstant or varies within a small tolerance with the operatingtemperature of the battery 102. The reference resistor 216 is optionallydisposed out of the battery 102 (e.g., in the internal circuit 106) orinside the battery 102.

In some implementations, the capacitor 210 is coupled in parallel withthe NTC thermistor 208, e.g., between the NTC terminal 230 and thesupply terminal 224. Referring to FIG. 2B, the capacitor 210 has an openarea 214 and two electrodes 212 a and 212 b that are at least partiallyexposed via the open area 214. In some implementations, the capacitor210 includes a capacitor with open metal gaps. In some implementations,the entire open capacitor 210 is not covered by an insulation material(e.g., a dielectric material) and exposed to air. In someimplementations, the capacitor 210 is covered by an insulation material(e.g., a dielectric material) that is partially removed on the open area214. In this example, the two electrodes 212 a and 212 b of thecapacitor 210 are interdigitated and formed with the same conductivelayer on a substrate, and partially overlap the open area 214.

In some situations, during normal operating conditions (e.g., under dryconditions, in the absence of any conductive liquid), the two electrodes212 a and 212 b of the capacitor 210 are electrically isolated from eachother, and do not provide any resistor to be coupled in parallel withthe NTC thermistor 208. Stated another way, when the open area 214 isexposed to air and no conductive liquid enters the open area 214, thetwo electrodes 212 a and 212 b are electrically decoupled in a directcurrent (DC) or low frequency domain, and the corresponding opencapacitor 210 has a predefined capacitance that is configured todetermine a high frequency response of the capacitor 210. As such, if aDC or low frequency voltage drop measured across the two terminals 230and 224 varies, the variation is not caused by conductive liquidentering the battery 102, but by a change of the operating temperatureof the battery 102.

In contrast, in some situations, conductive liquid 240 enters theelectronic device 100 and lands on the open area 214 of the capacitor210. A resistive path is formed from the conductive liquid 240 toelectrically couple the two electrodes 212 a and 212 b, therebyconverting the capacitor 210 to a resistor R_(C) having an equivalentresistance in the direct current or low frequency domain. The equivalentresistance of the resistor R_(C) converted from the capacitor 210 isdetermined based on at least a size of the open area 214, how the openarea 214 is covered by the conductive liquid 240, and an electricalresistivity of the conductive liquid 240. As a consequence of theconductive liquid 240 entering the open area 214, this resistor R_(C)converted from the capacitor 210 is coupled in parallel with the NTCthermistor 208, and in turn causes a change (e.g., a decrease) in avoltage drop across the NTC thermistor 208. Stated another way, in someimplementations, the presence of the conductive liquid 240 on thecapacitor 210 effectively places the resistor R_(C) in parallel with theNTC thermistor 208, and causes a drop in an effective resistance seenfrom two terminals 230 and 224 of the NTC thermistor 208.

In some implementations, the drop in the effective resistance seen fromthe two terminals 230 and 224 of the NTC thermistor 208 depends on aresistance value R_(NTC) of the NTC thermistor 208. For example, an NTCthermistor with a relatively large resistance value (e.g., 470k{circumflex over ( )}) has a higher degree of sensitivity to parallelresistance changes compared to another NTC thermistor that has a smallerresistance (e.g., 10 k{circumflex over ( )}). Additionally, it is notedthat when the conductive liquid 240 enters the open area 214, theeffective resistance seen from two terminals 230 and 224 of the NTCthermistor 208 is still configured to vary with a change of thetemperature of the battery 102, except that a sensitivity of theeffective resistance to the temperature of the battery 102 is distinctfrom (e.g., less than) a sensitivity of a resistance of the NTCthermistor 208 to the temperature of the battery 102. More details on atemperature sensitivity and a rate of a sensitivity variation of the NTCthermistor 208 are explained below with reference to FIGS. 8A and 8B.

The NTC thermistor 208 and the capacitor 210 are electrically coupled tocontrol circuit of the electronic device 100 (e.g., the internal circuit106), which is configured to detect a voltage drop across the NTCthermistor 208 and the capacitor 210, e.g., in the DC and low-frequencydomain. The internal circuit 106 is configured to determine whether thevoltage drop is caused by conductive liquid 240 electrically connectingthe two electrodes of the capacitor 210 or by an increase of theoperating temperature of the battery 102. In some implementations, theinternal circuit 106 determines whether the voltage drop is caused byconductive liquid electrically connecting the two electrodes of thecapacitor 210 by measuring a voltage drop across the NTC thermistor 208over time and determining an associated voltage drop rate. For example,the internal circuit 106 measures a time duration taken for a 10-90%voltage drop across the NTC thermistor 208 and determines the voltagedrop rate corresponding to the 10-90% voltage drop. Further, in someimplementations, the internal circuit 106 compares the voltage drop rateto a threshold voltage drop rate. The internal circuit 106 may determinethat the voltage drop is caused by conductive liquid electricallyconnecting the two electrodes of the capacitor 210 in accordance with adetermination that the voltage drop rate of the voltage is greater thanthe threshold voltage drop rate. Alternatively, in accordance with adetermination that the drop rate of the voltage is not greater than thethreshold drop rate, the internal circuit 106 may determine that thevoltage drop is caused by a temperature increase of one or more batterycells 120 of the battery 102. More details on detecting conductiveliquid in the battery 102 are explained below with reference to FIG. 7.

In some implementations, the electronic device 100 further includes areference NTC thermistor 218 that is packaged inside the battery 102 orproximate to the battery 102. Optionally, the reference NTC thermistor218 is part of the battery protection system 104. Optionally, thereference NTC thermistor 218 is located on the system side (e.g., aspart of the internal circuit 106) of the electronic device 100 and isisolated from the battery protection system 104. The reference NTCthermistor 218 is isolated from the NTC thermistor 208 and the capacitor210. As such, the reference NTC thermistor 218 is exposed to the samechange of the temperature of the battery 102, but not influenced byconductive liquid entering the open area of the capacitor 210 andelectrically connecting the two electrodes. The internal circuit 106 isconfigured to compare the effective resistances across the reference NTCthermistor 218 and the NTC thermistor 208 over time, to determinewhether any change of the effective resistance of the reference NTCthermistor 218 is caused by conductive liquid entering the battery 102or by the change of the temperature of the battery 102.

Specifically, in some implementations, the control circuit of theelectronic device 100 (e.g., internal circuit 106) is configured todetermine whether a voltage drop of the reference NTC thermistor 218remains substantially the same when a change of the effective resistanceof the NTC thermistor 208 is detected. If the voltage drop of thereference NTC thermistor 218 remains substantially the same, the changeof the effective resistance of the NTC thermistor 208 is caused byconductive liquid entering the battery 102. Alternatively, if thevoltage drop of the reference NTC thermistor 218 does not remainsubstantially the same and matches the change of the effectiveresistance of the NTC thermistor 208, the change of the effectiveresistance of the NTC thermistor 208 is caused by the change of thetemperature of the battery 102. Conversely, if the voltage drop of thereference NTC thermistor 218 neither remains substantially the same normatches the change of the effective resistance of the NTC thermistor208, the change of the effective resistance of the NTC thermistor 208may be caused by conductive liquid entering the battery 102.

In some implementations, the electronic device 100 (e.g., the internalcircuit 106) is configured to generate a message indicating that thebattery 102 has been exposed to the conductive liquid in accordance witha determination that the voltage drop across the NTC thermistor 208 andthe capacitor 210 is caused by conductive liquid entering the open areaof the capacitor 210 and electrically connecting the two electrodes.

FIG. 3 is a schematic diagram of another example rechargeable battery102 (also called a battery pack) having a battery protection system 104coupled to one or more battery cells 120, in accordance with someimplementations. The battery protection system 104 includes a PIC 202, aswitching component 206, and an NTC thermistor 208. The batteryprotection system 104 also includes another NTC thermistor 302 that iselectrically coupled in parallel with another open capacitor 304. Likethe capacitor 210, the capacitor 304 has an open area and two electrodesthat are at least partially exposed via the open area. The NTCthermistor 302 and the capacitor 304 are coupled to the PIC 202, e.g.,via an input 306 of the PIC 202. Control circuit (e.g., the PIC 202 orinternal circuit 106) is configured to detect a voltage drop across theNTC thermistor 302 and the capacitor 304 if conductive liquidelectrically connects the two electrodes that are at least partiallyexposed via the open area. Stated another way, the control circuit isconfigured to determine whether the voltage drop is caused by conductiveliquid entering the open area of the capacitor 304 and electricallyconnecting the two electrodes. Additionally, in some implementations,the battery protection system 104 includes the capacitor 210 coupled tothe NTC thermistor 208, and both of the capacitors 210 and 304 areconfigured to facilitate determining whether conductive liquid entersthe battery 102.

A serial resistor 308 is coupled in series with the one or more batterycells 120 and the switching component 206 along the charging anddischarging path 220 of the battery 102. In some implementations, theserial resistor 308 is immediately downstream of the one or more batterycells 120 on a direct current (DC) charging and discharging path 220(e.g., along the same current path that is going through the one or morebattery cells 120). In some implementations, the PIC 202 is coupled tothe serial resistor 308. The PIC 202 is configured to useinternal/integrated comparator logic to monitor a voltage drop on theserial resistor 308 (coupled to the PIC 202 via the inputs 312 and 314)and determine whether the one or more battery cells 120 are under anovercurrent or short circuit condition based on the voltage drop on theserial resistor 308. Alternatively, in some embodiments, the PIC 202 isconfigured to measure a battery voltage across the one or more batterycells 120 directly to detect an overvoltage or undervoltage condition.

In some implementations, the PIC 202 is configured to turn off acharging switch (e.g., switch 206 b of the switching component 206)arranged on the charging and discharging path 220 of the battery 102 todisable charging of the battery 102. In some situations, the chargingswitch 206 b is turned off in accordance with a determination that thebattery 102 is charged by an excessively large charging current based onthe voltage drop across the serial resistor 308 (i.e., under anovercharge or short circuit condition). In some situations, the chargingswitch 206 b is turned off in accordance with a determination that thebattery 102 is charged to an excessively large voltage (i.e., under anovervoltage condition). Likewise, in some implementations, the PIC 202is configured to turn off a discharging switch (e.g., switch 206 a ofthe switching component 206) arranged on the charging and dischargingpath 220 of the battery 102 to disable discharging of the battery 102.In some conditions, the discharging switch 206 a is turned off inaccordance with a determination that the battery 102 is discharging withan excessively large discharging current based on the voltage drop onthe serial resistor 308 (i.e., under an over-discharge or short circuitcondition. In some conditions, the discharging switch 206 a is turnedoff in accordance with a determination that the one or more batterycells 120 has an excessively low voltage (i.e., under an underchargedcondition).

In some implementations, the charging switch 206 b and the dischargingswitch 206 a are coupled in series with each other on the charging anddischarging path 220 of the battery 102. In some implementations, thePIC 202 is configured to control charging and discharging of the battery102 via the charging switch 206 b and the discharging switch 206 a,respectively, thereby protecting the battery 102 from an overcharge orovervoltage condition. In some implementations, each of the charging anddischarging switches 206 b and 206 a includes a transistor device havinga gate controlled by the PIC 202. In some other implementations, each ofthe charging and discharging switches 206 b and 206 a includes atransmission gate made of a pair of P-type and N-type transistors.

In some implementations, when conductive liquid enters the electronicdevice 100 and lands on the open area of the capacitor 304, the twoelectrodes of the capacitor 304 become electrically coupled, which inturn causes a decrease in an effective resistance of the NTC thermistor302 and a decrease in a voltage drop across the NTC thermistor 302. ThePIC 202 is configured to determine whether the decrease in the voltagedrop across the NTC thermistor 302 is caused by an increase of atemperature of the battery 102 or by the conductive liquid entering theopen area of the capacitor 304 and electrically connecting the twoelectrodes. Under some circumstances, the PIC 202 determines that thedecrease in the voltage drop across the NTC thermistor 302 is caused bya temperature increase of the battery 102 and that the temperature ofthe battery 102 exceeds a threshold temperature value. The PIC 202 isconfigured to deactivate charging or discharging of the battery 102(e.g., by disabling the charging switch 206 b and the discharging switch206 a) in accordance with a determination that the temperature of thebattery 102 exceeds the threshold temperature value. Similarly, undersome circumstances, the PIC determines that the decrease in the voltagedrop across the NTC thermistor 302 is caused by the conductive liquidentering the open area of the capacitor 304 and electrically connectingthe two electrodes, and deactivates charging or discharging of thebattery 102 (e.g., by disabling the charging switch 206 b and thedischarging switch 206 a).

FIG. 4 illustrates another example open capacitor 400 havinginterdigitated electrodes 402 and 404, in accordance with someimplementations. The capacitor 400 can be used as the capacitor 210 inFIG. 2 and/or the capacitor 304 in FIG. 3. The interdigitated electrodes402 and 404 are made on a single layer of conductive material 406 (e.g.,copper) with open gaps 408 interspersed between the conductive material406. The capacitor 400 has an open area 410, and the interdigitatedelectrodes 402 and 404 are at least partially exposed via the open area214. In some implementations, when the battery 102 having the capacitor400 is exposed to conductive liquid, the conductive liquid comes intocontact with and electrically couples (e.g., shorts) part of theinterdigitated electrodes 402 and 404 that are exposed on open area 410,thereby converting the capacitor 400 to a resistor R_(C) having anequivalent resistance in a DC or low frequency domain. When the resistorR_(C) converted from the capacitor 400 is coupled in parallel to the NTCthermistor 208 in FIG. 2 or the NTC thermistor 302 in FIG. 3, aneffective resistance of the NTC thermistor 208 or 302 is detected todrop, although no or little temperature increase occurs to the NTCthermistor 208 or 302 concurrently with the conductive liquid enteringthe open area 410 of the capacitor 400 and electrically connecting thetwo electrodes of the capacitor 400.

In some implementations not shown in FIG. 4, the open area 410 iscovered at least partially by a non-conductive liquid-absorbing material(e.g., a sponge). When the capacitor 400 is placed in a verticalorientation, the non-conductive liquid-absorbing material is configuredto keep liquid around the open area 410 and in proximity to theinterdigitated electrodes 402 and 404 for water ingress fault detection.Further, in some implementations, the non-conductive liquid-absorbingmaterial is extended from the open area 410 to another distinct locationwithin the battery 102 (e.g., a different side of or a remote locationon a protection circuit module), allowing the liquid that enters thebattery 102 to be absorbed at the distinct location and guided to theopen area 410 of the capacitor.

FIG. 5 is a schematic diagram of an electronic system 104 having abattery 102 coupled to a charger 502, in accordance with someimplementations. The battery protection system 104 includes aself-control protector (SCP) 504 configured to cut off a charging anddischarging path 510 in response to detection of an overcharge orovervoltage condition. In some implementations, the SCP 504 isconfigured to cut off a charging and discharging path 510 upon detectionof a voltage drop across an NTC thermistor 208 or 302 and acorresponding open capacitor 210 or 304 and in accordance with adetermination that the voltage drop is caused by conductive liquidentering the open area of the capacitor and electrically connecting thetwo electrodes of the capacitor.

The SCP 504 includes a fuse component (i.e., one of more fuses 506) anda heating element 508. The one or more fuses 506 are coupled in serieson a battery charging and discharging path 510 of the battery 102. Theheating element 508 is proximate to or under the one or more fuses 506,and controlled to heat up and melt the one or more fuses 506 upondetection of an overcharge or overvoltage condition or in accordancewith a determination that the voltage drop across the NTC thermistor 208or 302 is caused by the conductive liquid entering the open area of thecapacitor 210 or 304 and electrically connecting its two electrodes. Inan example, the heating element 508 is coupled in series with a fieldeffect transistor (FET) 512. Control circuit (e.g., the PIC 202) isconfigured to generate a fuse enable signal 514 to enable the FET 512 tocouple the heating element 508 to supply voltages. The heating element508 is heated up to melt down the fuses 506 and disconnect the batterycharging and discharging path 510 permanently.

FIG. 6 is a table 600 of example resistivity values of known conductiveliquid types, in accordance with some implementations. The table 600lists the resistivity values for pure water, distilled water, rainwater, tap water, river water, costal sea water, and open sea water.When one of these types of conductive liquid enters an open area of acapacitor 210 or 304, an equivalent resistance of a resistor R_(C)converted from the capacitor 210 or 304 is determined based on at leasta size of the open area, how the open area is covered by the conductiveliquid, and an electrical resistivity of the conductive liquid enteringthe open area and electrically connecting the two electrodes. A decreaseof an effective resistance of a corresponding NTC thermistor 208 or 302is further determined based on the equivalent resistance of a resistorR_(C) converted from a capacitor 210 or 304. Referring to FIG. 6, theequivalent resistance of the resistor R_(C) converted from the capacitor210 or 304 varies up to six orders based on the resistivity values ofthe conductive liquid types, so is the drop of the effective resistanceof the corresponding NTC thermistor 208 or 302 in some situations.

In some implementations, control circuit associated with the battery 102(e.g., the internal circuit 106 or PIC 202) is configured to determinethat the voltage drop across the NTC thermistor 208 or 302 and thecorresponding open capacitor is caused by conductive liquid entering theopen area of the capacitor and identify a type of conductive liquid inaccordance with such a determination. For example, the internal circuit106 may compare the voltage drop across the NTC thermistor 208 and thecapacitor 210 with a plurality of reference voltage drops. Eachreference voltage drop corresponds to a respective one of the knownconductive liquid types as illustrated in FIG. 6. The internal circuit106 identifies the type of the conductive liquid from the plurality ofknown conductive liquid types in accordance with the comparison.

In some implementations, the memory 112 is configured to store referencevalues (e.g., resistance values, resistivity values in FIG. 6, and/orvoltage drops) corresponding to the known conductive liquid types. Thecontrol circuit is configured to determine the plurality of referencevoltage drops based on the stored reference values. In one example, ifthe stored reference values are resistivity values, the internal circuit106 may generate the plurality of reference voltage drops by calculatingthe reference voltage drops based on the resistivity values directly orby using resistors having the resistivity values to match an impact ofthe conductive liquid. In another example, if the stored referencevalues are voltage drop values, the control circuit directly compare thevoltage drop across the NTC thermistor 208 or 302 and the capacitor withthe stored reference values.

FIG. 7 illustrates a temporal diagram 700 of an effective resistance ofan NTC thermistor 208 or 302 that is coupled in parallel with acapacitor 210 or 304, in accordance with some implementations. Theeffective resistance of an NTC thermistor 208 or 302 respondsdifferently in response to a temperature variation and conductive liquidentering an open area of the capacitor 210 or 304. The temperaturevariation occurs during an extended duration of time corresponding to afirst response time, while the conductive liquid impacts performance ofthe NTC thermistor 208 and open capacitor 210 instantaneously, i.e., ina short instant corresponding to a second response time that is lessthan the first response time. In some implementations, a thresholdresponse time or a threshold drop rate is defined, and a voltage dropacross the NTC thermistor 208 or 302 is monitored. A response time or atemporal drop rate of the voltage drop across the NTC thermistor 208 or302 is compared with the predefined threshold response time or temporaldrop rate to determine whether the voltage drop is caused by conductiveliquid or a temperature increase.

In an example, the voltage drop 702 across the NTC thermistor 208 andopen capacitor 210 decreases by 0.25 V due to an increase of 25° C. inthe temperature of the battery 102. This voltage drop occurs graduallyand lasts for approximately four hours. In contrast, the voltage drop704 across the NTC thermistor 208 and open capacitor 210 decreases by0.25 V due to conductive liquid entering the capacitor 210. This voltagedrop 704 occurs within the short instant and lasts for less than aminute. An example threshold response time is 1 minute for acharacteristic voltage drop of 0.5 V or for a 10-90% voltage drop, andan example drop rate is 1 V/minute. Any voltage drop having a responsetime shorter than the threshold response time or a temporal drop ratefaster than the threshold drop rate is determined to be caused by anevent of conductive liquid entering the battery 102.

Specifically, in some implementations, the temporal drop rate of thevoltage drop across the NTC thermistor 208 and open capacitor 210 iscompared to a threshold drop rate. In accordance with a determinationthat the temporal drop rate of the voltage is greater than the thresholddrop rate, the control circuit of the electronic device 100 determinesthat the voltage drop is caused by conductive liquid entering the openarea of the capacitor and electrically connecting the two electrodes ofthe capacitor. Conversely, in accordance with a determination that thetemporal drop rate of the voltage is not greater than the threshold droprate, the control circuit of the electronic device 100 determines thatthe voltage drop is caused by a temperature increase of the one or morerechargeable battery cells of the battery 102.

FIG. 8A is a diagram 800 of an effective resistance of an NTC thermistor208 or 302 that varies with a temperature, in accordance with someimplementations, and FIG. 8B is a diagram 850 of a temperaturesensitivity of an NTC thermistor 208 or 302 that varies with atemperature, in accordance with some implementations. Curves 802 and 852represent the effective resistance and temperature sensitivity of theNTC thermistor itself as a function of a temperature of the battery 102,respectively. When a capacitor coupled in parallel to the NTC thermistoris converted to a resistor R_(C) due to conductive liquid entering thebattery 102, curves 802 and 854 go down to Curves 804 and 854, whichrepresent the effective resistance and temperature sensitivity of acombination of the NTC thermistor and open capacitor as a function ofthe temperature of the battery 102, respectively. As such, whenconductive liquid enters the battery 102, a voltage across the NTCthermistor and open capacitor drops and responds differently to thetemperature of the battery 102, compared with when no conductive liquidenters the battery 102.

Referring to FIG. 8A, in some implementations, when conductive liquidenters the battery 102 at a given temperature, the effective resistanceof the NTC thermistor drops from a point 802A on the curve 802 to apoint 804A on the curve 804. The curve 802 has a point 802B that matchesthe effective resistance with the point 804A, and therefore, it needs tobe determined whether the effective resistance drops due to atemperature increase of the battery 102 or the conductive liquidentering the battery. Alternatively, in some implementations, a lowresistivity conductive liquid enters the battery 102. The effectiveresistance of the NTC thermistor drops from the point 802A on the curve802 to a point 806 below a resistance drop limit 808. The resistancedrop limit 808 is less than the effective resistance of the NTCthermistor on the curve 802 at least up to a temperature limit (e.g.,100° C.) which is rarely reached by the battery 102. That said, in somesituations, the control circuit of the electronic device 100 identifiesa voltage drop limit corresponding to a temperature increase of the oneor more rechargeable battery cells, e.g., the voltage drop limitcorresponds to the resistance drop limit 808 and is at least lower thana voltage drop across the NTC thermistor at the temperature limit. Avoltage drop across the NTC thermistor and the capacitor is comparedwith the voltage drop limit. If the voltage drop is caused by thetemperature increase, it never reaches the voltage drop limit. As such,in accordance with a determination that the voltage drop exceeds thevoltage drop limit, the control circuit of the electronic device 100 candetermine that the voltage drop is caused by conductive liquid enteringthe battery 102 rather than by the temperature variation of the battery102.

Referring to FIG. 8B, when an NTC thermistor 208 or 302 is applied in abattery protection system 104, its temperature sensitivity 852 and rateof a sensitivity variation with respect to a temperature are known. Whena capacitor coupled in parallel to the NTC thermistor is converted to aresistor R_(C) due to conductive liquid entering the battery 102, thecurve 852 corresponding to the temperature sensitivity of the NTCthermistor 208 or 302 shifts to another curve (e.g., to the curve 854).In some implementations, the control circuit of the electronic device100 monitors a temperature sensitivity of a voltage drop across the NTCthermistor and open capacitor or a rate of the sensitivity variationwith respect to the temperature of the battery 102. In accordance with adetermination that the temperature sensitivity or the rate of thesensitivity variation of the voltage drop does not match the sensitivitycurve 852, the control circuit of the electronic device 100 determinesthat the voltage drop is caused by conductive liquid entering thebattery 102 (specifically, the open area of the capacitor 210 or 304).

FIG. 9 is a flowchart of an example method 900 of detecting conductiveliquid in a rechargeable battery 102, in accordance with someimplementations. An NTC thermistor 208 or 302 and a capacitor 210 or 304are proximate to one or more rechargeable battery cells 120 of therechargeable battery 102. A voltage drop across the NTC thermistor andcapacitor is received (902). The capacitor 210 or 304 has (904) an openarea and two electrodes that are at least partially exposed via the openarea, and the two electrodes are electrically isolated. It is thendetermined (906) whether the voltage drop is caused by conductive liquidthat electrically connects the two electrodes that are at leastpartially exposed via the open area of the capacitor.

In some implementations, in accordance with a determination that thevoltage drop across the NTC thermistor and the capacitor is caused byconductive liquid electrically connecting the two electrodes of thecapacitor, a message is generated to indicate that the one or morerechargeable battery cells have been exposed to the conductive liquid.In some implementations, a fuse component 506 is coupled on a batterycharging and discharging path of the one or more rechargeable batterycells 120. In accordance with a determination that the voltage drop iscaused by the conductive liquid electrically connecting the twoelectrodes of the capacitor, a fuse enable signal is generated toactivate the fuse component to disconnect the battery charging anddischarging path permanently. In some implementations, a temporal droprate is determined for the voltage drop across the NTC thermistor andthe capacitor. Whether the voltage drop is caused by conductive liquidor a temperature increase is determined based on the temporal drop rateof the voltage drop.

It should be noted that details described with respect to FIGS. 1-8 arealso applicable in an analogous manner to the method 900 described abovewith respect to FIG. 9. For brevity, these details are not repeatedhere.

The terminology used in the description of the various describedimplementations herein is for the purpose of describing particularimplementations only and is not intended to be limiting. As used in thedescription of the various described implementations and the appendedclaims, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Additionally, it will be understood that,although the terms “first,” “second,” etc. may be used herein todescribe various elements, these elements should not be limited by theseterms. These terms are only used to distinguish one element fromanother.

As used herein, the term “if” is, optionally, construed to mean “when”or “upon” or “in response to determining” or “in response to detecting”or “in accordance with a determination that,” depending on the context.Similarly, the phrase “if it is determined” or “if [a stated conditionor event] is detected” is, optionally, construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event]” or “in accordance with a determination that [astated condition or event] is detected,” depending on the context.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific implementations. However, theillustrative discussions above are not intended to be exhaustive or tolimit the claims to the precise forms disclosed. Many modifications andvariations are possible in view of the above teachings. Theimplementations were chosen and described in order to best explainprinciples of operation and practical applications, to thereby enableothers skilled in the art.

Although various drawings illustrate a number of logical stages in aparticular order, stages that are not order dependent may be reorderedand other stages may be combined or broken out. While some reordering orother groupings are specifically mentioned, others will be obvious tothose of ordinary skill in the art, so the ordering and groupingspresented herein are not an exhaustive list of alternatives. Moreover,it should be recognized that the stages can be implemented in hardware,firmware, software or any combination thereof.

What is claimed is:
 1. An electronic device, comprising: one or morerechargeable battery cells; a negative temperature coefficient (NTC)thermistor proximate to the one or more rechargeable battery cells; acapacitor coupled in parallel with the NTC thermistor, the capacitorhaving an open area and two electrodes that are at least partiallyexposed via the open area, wherein the two electrodes are electricallyisolated; and control circuit coupled to the NTC thermistor and thecapacitor, wherein the control circuit is configured to detect a voltagedrop across the NTC thermistor and the capacitor if conductive liquidelectrically connects the two electrodes that are at least partiallyexposed via the open area.
 2. The electronic device of claim 1, whereinthe control circuit is configured to: in accordance with a determinationthat the voltage drop across the NTC thermistor and the capacitor iscaused by conductive liquid electrically connecting the two electrodesof the capacitor, generate a message indicating that the one or morerechargeable battery cells have been exposed to the conductive liquid.3. The electronic device of claim 1, wherein the two electrodes of thecapacitor are interdigitated and formed with the same conductive layeron a substrate, and at least partially overlap the open area.
 4. Theelectronic device of claim 1, further comprising: a fuse componentcoupled on a battery charging and discharging path of the one or morerechargeable battery cells; wherein the control circuit is configured toin accordance with a determination that the voltage drop is caused bythe conductive liquid electrically connecting the two electrodes of thecapacitor, generate a fuse enable signal to activate the fuse componentto disconnect the battery charging and discharging path permanently. 5.The electronic device of claim 1, the control circuit is furtherconfigured to: determine a temporal drop rate of the voltage drop acrossthe NTC thermistor and the capacitor; and determine whether the voltagedrop is caused by conductive liquid or a temperature increase based onthe temporal drop rate of the voltage drop.
 6. The electronic device ofclaim 5, wherein determining whether the voltage drop is caused by theconductive liquid or the temperature increase further comprises:comparing the temporal drop rate of the voltage to a threshold droprate; in accordance with a determination that the temporal drop rate ofthe voltage is greater than the threshold drop rate, determining thatthe voltage drop is caused by conductive liquid electrically connectingthe two electrodes of the capacitor; and in accordance with adetermination that the temporal drop rate of the voltage is not greaterthan the threshold drop rate, determining that the voltage drop iscaused by a temperature increase of the one or more rechargeable batterycells.
 7. The electronic device of claim 1, wherein the control circuitis further configured to: identify a voltage drop limit corresponding toa temperature increase of the one or more rechargeable battery cells;compare the voltage drop across the NTC thermistor and the capacitorwith the voltage drop limit; and determine whether the voltage dropexceeds the voltage drop limit.
 8. The electronic device of claim 1,wherein the control circuit is further configured to: in accordance witha determination that the voltage drop across the NTC thermistor and thecapacitor is caused by the conductive liquid electrically connecting thetwo electrodes of the capacitor, identify a type of the conductiveliquid.
 9. The electronic device of claim 8, wherein identifying thetype of the conductive liquid further comprises: comparing the voltagedrop with a plurality of reference drops, each reference dropcorresponding to a respective one of a plurality of known conductiveliquid types; and in accordance with a comparison result, identifyingthe type of the conductive liquid from the plurality of known conductiveliquid types.
 10. The electronic device of claim 9, further comprisingmemory for storing a plurality of reference values corresponding to theplurality of known conductive liquid types, and the control circuit isconfigured to determine the plurality of reference drops based on theplurality of reference values.
 11. The electronic device of claim 1,further comprising a reference NTC thermistor proximate to the one ormore rechargeable battery cells, wherein the control circuit is furtherconfigured to determine whether a voltage drop of the reference NTCthermistor remains substantially the same.
 12. A battery protectioncircuit, coupled to one or more rechargeable battery cells, comprising:a first negative temperature coefficient (NTC) thermistor proximate tothe one or more rechargeable battery cells; a capacitor coupled inparallel with the NTC thermistor, the capacitor having an open area andtwo electrodes that are at least partially exposed via the open area,wherein the two electrodes are electrically isolated; and a controlcircuit coupled to the NTC thermistor and the capacitor, wherein thecontrol circuit is configured to detect a voltage drop across the NTCthermistor and the capacitor if conductive liquid electrically connectsthe two electrodes that are at least partially exposed via the openarea.
 13. The battery protection circuit of claim 12, furthercomprising: a reference NTC thermistor proximate to the one or morerechargeable battery cells, wherein the control circuit is furtherconfigured to determine whether the voltage drop across the NTCthermistor and the capacitor is consistent with a voltage drop acrossthe reference NTC thermistor.
 14. The battery protection circuit ofclaim 12, further comprising: a switching component coupled in serieswith the one or more rechargeable battery cells on a battery chargingand discharging path, the battery protection circuit configured tocontrol the switching component to manage charging and discharging ofthe one or more rechargeable battery cells via the battery charging anddischarging path.
 15. The battery protection circuit of claim 14,wherein the battery protection circuit is configured to control theswitching component to disable charging and discharging of the one ormore rechargeable battery cells when the voltage drop across the NTCthermistor and the capacitor exceeds a threshold voltage drop.
 16. Thebattery protection circuit of claim 12, wherein the two electrodes ofthe capacitor are interdigitated and formed with the same conductivelayer on a substrate, and at least partially overlap the open area. 17.A method, comprising: receiving a voltage drop across an NTC thermistorand a capacitor that are proximate to one or more rechargeable batterycells, wherein the capacitor has an open area and two electrodes thatare at least partially exposed via the open area, and the two electrodesare electrically isolated; and determining whether the voltage drop iscaused by conductive liquid that electrically connects the twoelectrodes that are at least partially exposed via the open area of thecapacitor.
 18. The method of claim 17, further comprising: in accordancewith a determination that the voltage drop across the NTC thermistor andthe capacitor is caused by conductive liquid electrically connecting thetwo electrodes of the capacitor, generating a message indicating thatthe one or more rechargeable battery cells have been exposed to theconductive liquid.
 19. The method of claim 17, wherein a fuse componentis coupled on a battery charging and discharging path of the one or morerechargeable battery cells, the method further comprising: in accordancewith a determination that the voltage drop is caused by the conductiveliquid electrically connecting the two electrodes of the capacitor,generating a fuse enable signal to activate the fuse component todisconnect the battery charging and discharging path permanently. 20.The method of claim 17, further comprising: determining a temporal droprate of the voltage drop across the NTC thermistor and the capacitor;and determining whether the voltage drop is caused by conductive liquidor a temperature increase based on the temporal drop rate of the voltagedrop.